Single or multiple stage blower fans attached to the rotor of a generator are used for feeding a cooling medium in electrical generators. Blower blades are connected to the rotor of electrical generators in a variety of ways. Threaded connections between the rotor and blade root are known in the art. Threaded connections are simple and easy to assemble. However, the stress levels and cyclic loads can lead to damages in the threaded connection. In particular the first threads on the root of the blade are subject to high cyclic load changes which can cause failure due to fatigue.
A repair method is known in the art which re-establishes a fatigue limit within an assembly having an aluminum component that has become cracked or contains fatigued material. Such an assembly may include an aluminum blade having an aluminum blade root and is connected to a steel blower hub. For repairing the forming of threads on a first diameter of the blade root; which is smaller than the original diameter of the blade root is proposed. To reassemble the blades a securing collar is secured in the hole formed in the blower hub. The collar comprises internal threads for receiving the threads formed on the first diameter of the blade root; and the blade root of the rotor blade is screwed into the collar.
The re-machined blade root has a smaller diameter than the original blade root and thus the strength of the root is reduced. Even if damaged material might have been removed, the re-established fatigue limit time is typically below the life time of an original new part because of the reduced root diameter. In addition an exact alignment of the recut thread on the blade root with the blade axis is difficult and time consuming. In particular during an outage on site this can pose serious practical problems and potentially leads to misaligned or damaged blades.